Method for securing the lubrication of bearings in a hermetic high-speed machine

ABSTRACT

The present invention is directed to a method for operating a hermetic, small-size power plant in which a primary circulation is conducted in a main line connecting a high-speed machine including at least a turbine and a generator installed on a joint rotor, a vaporizer and a condenser. Fluid lubrication of bearings of the rotor during the continuing operation is effected by fluid medium passing through the condenser and along the main line of the primary circulation. The vaporizer is connected to the high-speed machine through medium flow paths defining a circulating medium circuit bypassing the condenser and at least partly bypassing the main line of the primary circulation to secure passage of circulating medium accumulated in the vaporizer for lubrication of the bearings of the rotor during stopping of the primary circulation.

FIELD OF THE INVENTION

The present invention relates to a method in a hermetic small-size powerplant, especially in one based on the Organic Rankine Cycle (ORC)process, comprising a system consisting of a high-speed machine,vaporizer, and condenser which are connected by a main line foreffecting the primary circulation, wherein the high-speed machinecomprises a turbine, a generator and possibly a main feed pump mountedon a joint rotor, and in which the bearing of the rotor is arranged tobe lubricated by fluid lubrication and particularly in a situation ofcontinuing operation of the process through the condenser along the mainline of primary circulation.

BACKGROUND OF THE INVENTION

The small-size power plant based on the ORC process was developedespecially for the recovery of waste heat from various heat-producingprocesses or machines where, due to the temperature of the waste heat ordue to the circumstances of the environment, waste heat cannot be usedas such or by means of heat exchangers or corresponding means. In asmall-size power plant, waste heat is converted generally by a turbineto electricity which is easily used for different purposes.

It can be shown thermodynamically that the Organic Rankine Cycle processis the best applicable method for this kind of energy converting. Theheat of vaporization of an organic substance is low in relation to forexample, the heat of evaporation of water, and its fall of specificenthalpy in the turbine is small and the mass flow rate in relation tothe output is high, and it is possible to reach a high turbineefficiency even in a range of small capacity.

A hermetic or fully closed-circuit process has the advantage that thereare no leaks and the process is thus reliable and durable in operation.

The utilization of high-speed technology, wherein the turbineis-directly coupled with a generator rotating at the same speed and thusproducing high-frequency current, has made it possible to furthersimplify the process such that e.g. a separate reduction gear requiredby conventional processes as well as shaft inlets are not needed.

A hermetic energy converter of this kind, operating on high-speedtechnology and based on the ORC process, is known from the publicationFI-66234, according to which the bearing of the rotor of the high-speedmachine is lubricated by an organic circulating medium, wherein thecirculating medium is in a gaseous state. Thus it is possible to reach avery high efficiency, because the losses of gaseous bearing are verysmall. However, for reasons of manufacturing techniques, bearingslubricated with fluid circulating medium have been shown to be morecost-saving.

The use of the circulating medium in a liquid state in the said bearingsystem is known for example from U.S. Pat. No. 2,961,550 which relatesto the bearings of a power plant lubricated by a circulating medium,with special respect to starting up a power plant. According to thepublication, the said bearing system is effected by condensating thecirculating medium from a gaseous state into a liquid state by aseparate condenser, whereafter the fluid circulating medium is directedto the bearings. With particular attention to starting up the powerplant, its bearing pipework is equipped with a valve that operates onthe basis of the pressure of the circulating medium and opens at anessentially lower pressure than the main valve in the pipework of theprimary circulation, wherein the lubrication of bearings starts beforethe start of the turbine.

In the small-size power plant or energy converter systems in use, aproblem has arisen in connection with different stoppage situations dueto disturbances, failures and corresponding reasons when the primarycirculation to the turbine must be discontinued and the lubrication ofthe bearings of the rotor in the high-speed machine in the presentsystems is discontinued or significantly reduced during a stoppingsituation. Thus the technique used, by which the rotor generally rotatesat the synchronous speed of the network (3000 rpm), results ininsufficient lubrication which wears down the bearings and essentiallyreduces their time of use.

The method according to this invention makes it possible to obtain adecisive improvement to the disadvantages presented above and thus toraise the level of technology in the field. To reach this objective, itis characteristic to the method according to this invention that in astoppage situation of the primary circulation in the main line of theprocess, the fluid lubrication of the bearings of the rotor is arrangedfrom the vaporizer of the energy converter, such as from a boiler, aprocess furnace, a ceramic furnace or corresponding, by means ofpressurized circulating medium accumulated in the vaporizer.

One of the most important advantages of the method according to theinvention is the essentially longer uninterrupted duty cycles of thehigh-speed machine, and thus also of the entire energy converter, aswell as the essentially longer time of use of the bearings of the saidrotor. Also, the controllability of the entire process of the energyconverter in a stoppage situation is essentially improved.

The following explanation demonstrates the invention in detail and alsorefers to the attached drawings wherein

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 shows an operating diagram of a first embodiment of the methodaccording to the present invention in a typical ORC process inprinciple, and

FIG. 2 shows an alternative operating diagram of a second embodiment ofthe method according to the invention in a typical ORC process inprinciple.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The method according to the present invention is intended forapplication in processes similar to those presented in FIGS. 1 and 2,wherein the primary circulation 10 of the small-size power plant or theenergy converter is effected in such a way that evaporator 11, such as aboiler, process furnace, ceramic furnace or the like evaporates theorganic circulating medium, such as different Freons or toluene, whichfurther expands in turbine 3, is condensated in condenser 21, and isreturned by pump/pumps 5, 12, 13, 14 to evaporator 11 wherein the flowof circulating medium during the normal drive of the process to theturbine is controlledby adjusting the main operating valve 18 and/or theoperating valve 19. Theheat energy produced by the evaporator 11 in thecirculating medium is converted in the high-speed machine 1 by generator4 which rotates at the same speed as turbine 3 into high-frequencyelectricity which is further rectified/inverted in the furtherprocessing 20 to-be-applicable for lateruses. In the normal drive, thehydrodynamic bearings 6 are lubricated by the fluid circulating mediumalong the pipeline 8 from the pressure side of pump 12 or 14.

Because the organic medium, contrary to steam, is usually superheatedwhen expanded, the efficiency of the process can be further improvedwith respect to the applications presented by installing a separatepreheater or recuperator between turbine 3 and vaporizer 11. The numberof pumps needed in the process depends on the pressure level of thecirculating medium, which is affected by the features of the circulatingmedium used, the temperature of the heating gas flow A, the heightdifferences of the pipework in the process and other correspondingfactors, in which case, with low pressure level, the feed pump 5connected to rotor 2 of the turbine 3 and generator 4 is not necessarilyneeded in the high-speed machine 1.

In practice, a permanently magnetized generator, presented in a greaterdetail in the publication FI-71640, has been used as generator 4.Furthermore, it is practical to use as bearings 6 hydrodynamicrolling-segment type bearings, whose structure and operating principleis presented in more detail for example in the publication Glacier:Tilting Pod Journal Bearings, Designers Handbook No. 10.

In a typical ORC process according to FIG. 1, the method according tothe present invention is realized in such a way that in a stoppagesituation of the primary circulation of the main line 10, wherein themain operational valve 18 in the main line 10 is closed, the temperaturedevelopment in vaporizer 11 continues, and the circulating mediumaccumulated in the vaporator is vaporized. Because of evaporation, thepressure level of the circulating medium rises in vaporizer 11. The risein the pressure level results in the discharge of the circulating mediumin a liquid state at the inlet side 11b of the vaporizer and its furtherpassage controlled by the barrier member (valve) 15a in the main line 10from the branch point 10a of the main line to the flow path 7 whichdischarges into fluid ejector 12. By the action of fluid ejector 12, thecirculating medium passes further, when the pre-feed pump 13 is stoppedand the operating valve 19 closed, from the branch point 10b of the mainline via the second flow path 8 to the bearings 6 of rotor 2, and afterlubrication at the third flow path 9 back to the suction side of thefluidejector 12 of main line 10. The flow paths 7 and 8 operate as flowpaths conveying circulating medium to the high-speed machine with thepurpose oflubrication, and the third flow path 9 operates as a flow pathfor returning circulating medium acting as a lubricant from thehigh-speed machine.

In accordance with the general principles of measurement in thecirculationprocess, the inner volume of vaporizer 11 containingcirculating medium is related to the inner volumes of the flow paths 7,8, 9 and the bearings 6 in such a way that after closing of the mainoperating valve 18, a possible stoppage of operation of vaporizer 11which is due to an increasein pressure and/or temperature of thecirculating medium accumulated in vaporizer 11, and which is effected byan inner safety device in vaporizer11, such as a guard for boiling dryor corresponding, occurs essentially later than closing of the mainoperational valve 18. The lubrication of bearings 6 is secured for thetime required for stopping rotor 2, in practice for at least 30 secondsafter the closing of the main operationalvalve 18. In the most commonsystems, the volume of vaporizer 11 is manifold as compared with thestopping stage which normally takes about 30seconds. Thus the circuitprovides for the fluid lubrication of bearings during the stopping ofthe rotor in all failure situations.

In a typical ORC process according to FIG. 2, the method according tothe invention is realized in an altenative way that in a stoppagesituation ofthe primary circulation of the main line 10 (for examplewhen pre-feed pump14 stops), wherein the main operational valve 18 inthe main line 10 is closed, the temperature development in vaporizer 11continues, wherein thecirculating medium accumulated in the vaporizer isvaporized. Because of evaporation, the pressure level of the circulatingmedium rises in such vaporizer 11 in a way that the pressure level ishighest at the outlet side 11a and lowest at the inlet side 11b. Therise in pressure level results in the discharge of the circulatingmedium in a liquid state from the inlet side 11b of the vaporizer andits passage by the barrier member 15a in the main line 10 from thebranch point 10a of the main line via thefirst flow path 7 to the branchpoint 10b on the pressure side of the pre-feed valve 14 in the main line10, wherein the pressure level of the circulating medium is adjusted bymeans 17 in the flow path 7, such as a pressure reducing valve orcorresponding. From the branch point 10b of themain line, thecirculating medium is further conveyed by pressure and directed bybarrier member 15b between the branch point 10b and pre-feed pump 14through the second flow path 8 to the bearings 6 of rotor 2, and afterlubrication by the third flow path 9 back to the suction side ofpre-feed pump 14 of main line 10. Because of the general principles oftheconstruction of the circulating process, the inner volume ofvaporizer 11 containing circulating medium is related to the innervolumes of flow paths (circuits) 7, 8, 9 and bearings 6 such that afterthe main operational valve 18 is closed, a possible operational stoppageof either vaporizer 11, due to the increase of pressure and/ortemperature of the circulating medium accumulated in vaporizer 11 by aninner safety device in vaporizer 11, such as a guard for boiling dry, ora stoppage of the flow through the first flow path 7 by means 16 in thefirst flow path 7, such as a temperature-controlled valve orcorresponding, takes place essentially later than the closing of themain operational valve 18, and the fluid lubrication of the bearings 6is secured for the time of stopping of rotor 2, in practice at least 30seconds after the closing of the main operational valve 18. Thus thecircuit provides for the fluid lubrication of bearings during thestopping of the rotor in all failure situations.

It is obvious that the present invention is not limited to theapplicationspresented above, but it can be modified within the basicidea even to a great extent. For instance, the circulating mediumaccumulated in the vaporizer can be used in a vaporized state, whereinthe vapor, for exampleaccording to U.S. Pat. No. 2,961,550 mentionedabove, is condensated by condenser 21 or by a separate condenser intothe liquid state, whereafter the fluid circulating medium is conveyed tothe bearings according to the present invention. It should also be notedthat the drawings presented areprimarily operational embodiments inprinciple, wherein the pipework equipment-may in practical applicationsvary or be more complete as to thevalves, pumps, and the line.

I claim:
 1. A method for operating a hermetic, small-size power plant,including the steps of:a) conducting a primary circulation in a mainline connecting a high-speed machine including at least a turbine and agenerator installed on a joint rotor, a vaporizer and a condenser; b)effecting fluid lubrication of bearings of the rotor during thecontinuing operation by fluid medium passing through the condenser andalong the main line of the primary circulation; c) connecting thevaporizer to the high-speed machine through medium flow paths defining acirculating medium circuit and bypassing the condenser and at leastpartly bypassing the main line of the primary circulation to securepassage of circulating medium accumulated in the vaporizer forlubrication of the bearings of the rotor during stopping of the primarycirculation.
 2. Method according to claim 1, furthercomprising:providing a branch point between the high-speed machine andthe inlet side of the vaporizer in the main line; arranging a barriermember in connection with the branch point of the main line, to preventthe flow of circulating medium in the direction of the high-speedmachine in the main line; connecting to the branch point the inlet sideof the fluid flow path circuit for passing circulating medium to thehigh-speed machine; connecting the outlet side of the circulating mediumflow circuit to the bearings; and returning to circulating medium fromthe high-speed machine to the main line through the circulating mediumfluid flow circuit.
 3. Method according to claim 1, further comprisingthe steps of:arranging a branch point between the high-speed machine andthe inlet side of the vaporizer in the main line; providing a barriermember connected to the branch point of the main line, the barrierdirection of which is such that it prevents the flow of circulatingmedium in the direction of the high-speed machine in the main line;connecting the inlet side of a first flow path of the circuit to thebranch point and the outlet side of said first flow path to means forconveying circulating medium to the high-speed machine; and conveyingthe circulating medium by said means for conveying circulating medium tothe bearings of the high-speed machine using a second flow path of thecircuit.
 4. Method according to claim 1, wherein the pressurizedcirculating medium accumulated in the vaporizer in a liquid state ispassed by a first fluid flow path of the circuit to a fluid ejectoroperating as a device for conveying circulating medium in such a waythat it pumps the lubricating fluid for the bearings lubrication byusing a second fluid flow path.
 5. Method according to claim 4, whereinthe inlet side of the second fluid flow path of the circulating mediumcircuit is arranged between a pre-feed pump located after the fluidejector in the direction of flow of the circulating medium in the mainline, and wherein the operation of the pre-feed pump is controlled anddiscontinued and the flow of the circulating medium to the pre-feed pumpis prevented by a reflux valve.
 6. Method according to claim 1, whereinpressurized circulating medium accumulated in the vaporizer in a liquidstate is passed by a first fluid flow path of the circuit to thepressure side of a pre-feed pump operating as a device for conveyingcirculating medium to the main line.
 7. Method according to claim 6,wherein at least one member is arranged between the main line and abranch point of the second fluid flow path, and in between the main lineand a branch point of the outlet side of a third fluid flow path of thecircuit in the main line operating against the normal flow direction ofthe circulating medium.
 8. Method according to claim 3, wherein at leastone member for controlling the pressure of the circulating medium, isarranged in the first fluid flow path.
 9. Method according to claim 3,wherein at least one element for limiting the temperature of thecirculating medium, is arranged in the first fluid flow path.
 10. Methodaccording to claim 1, wherein the inner volume of the vaporizercontaining circulating medium is so arranged in relation to the innervolumes of said fluid flow paths and the bearings that after closing ofa main operational valve, the stoppage of the operation of thevaporizer, due to the rise of at least one of pressure and temperatureof the circulating medium accumulated in the vaporizer, and the stoppageof fluid flow through the medium flow paths takes place essentiallylater than the closing of the main operational valve, to thereby securelubrication of the bearings during the stoppage of the rotor.
 11. Methodaccording to claim 7, wherein said at least one member is a one-wayvalve.
 12. Method according to claim 8, wherein said pressurecontrolling member is a pressure-reducing valve.
 13. Method according toclaim 9, wherein said temperature limiting element is atemperature-controlled valve.